We're accustomed to thinking geologic history has an extremely long, slow time scale. But in recent years Nobel Laureate atmospheric researcher Paul Crutzen and other scientists have proposed that human activity is changing the planet pervasively and permanently. As a result, they suggest, we've said goodbye to the Holocene epoch, which began 11,700 years ago at the end of the last Ice Age, and entered into a new, man-made Anthropocene epoch.
In a newly published study, Earth scientists Jan Zalasiewicz and Mark Williams, of the University of Leicester, and Colin Waters, of the British Geological Survey, bolster the case for an Anthropocene epoch by pointing out that human activities -- ranging from fracking for oil and gas to underground nuclear tests -- actually have created profound changes deep beneath the Earth's surface.
"Many of these underground transformations, being beyond the reach of surface erosion, will effectively last forever," Williams said in a release. "They can be preserved for millions and even billions of years into the future, and thus may form our most enduring -- and most puzzling -- legacy, for any intelligent creatures that may inherit the Earth from us."
The worry is that such changes may combine with climate change and chemical alteration of the oceans to create an environment that's less and less hospitable to life, including humans.
Here are six ways in which humans have changed the planet beneath its surface.